Implantable medical devices (IMDs), including cardiac rhythm management devices such as pacemakers and implantable cardioverter/defibrillators, typically have the capability to communicate data with an external device called an external programmer via a radio-frequency telemetry link. One use of such an external programmer is to program the operating parameters of an implanted medical device. For example, the pacing mode and other operating characteristics of a pacemaker are typically modified after implantation in this manner. Modern implantable devices also include the capability for bidirectional communication so that information can be transmitted to the programmer from the implanted device. Among the data that may typically be telemetered from an implantable device are various operating parameters and physiological data, the latter either collected in real-time or stored from previous monitoring operations.
External programmers are commonly configured to communicate with an IMD over an inductive link. Coil antennas in the external programmer and the IMD are inductively coupled so that data can be transmitted by modulating a radio-frequency carrier waveform which corresponds to the resonant frequency of the two coupled coils. An inductive link is a short-range communications channel requiring that the coil antenna of the external device be in close proximity to the IMD, typically within a few inches. Other types of telemetry systems may utilize far-field electromagnetic radiation or other types of data links such as telephone lines or networks (including the internet) to enable communications over greater distances. Such long-range telemetry allows the implantable device to transmit data to a remote monitoring unit or be programmed from a remote location. Long-range telemetry thus allows physicians to monitor patients and to conduct patient follow-ups from across the room or even across the world.
Long-term telemetry for implantable medical devices, however, causes some special concerns which are not present with short-range telemetry. Communication with an implantable device over a short-range communications channel such as an inductive link requires that the external device be near the patient, so that the clinician knows whose implantable device is being programmed and the patient knows who is programming and receiving data from the implantable device. Long-range telemetry, on the other hand, does not require such physical proximity and allows the possibility of a physician inadvertently programming the wrong device. Communications with far-field electromagnetic radiation or over some kind of network also allows the communications to be intercepted by an unintended user, raising privacy concerns for the patient. A malicious user might even try to use the long-range telemetry system to re-program an implanted device. The present invention is a system and method for providing long-range telemetry which addresses these concerns.